Problem: The arithmetic sequence $(a_i)$ is defined by the formula: $a_i = 3 + 3(i - 1)$ What is $a_{12}$, the twelfth term in the sequence?
Answer: From the given formula, we can see that the first term of the sequence is $3$ and the common difference is $3$ To find $a_{12}$ , we can simply substitute $i = 12$ into the given formula. Therefore, the twelfth term is equal to $a_{12} = 3 + 3 (12 - 1) = 36$.